My long term goal is to understand the production of behaviors at the cellular level. Generation and modulation of coordinated rhythmic behaviors is a necessity for most organisms. For years, the crustacean STG has been a premier system for studying the modulation of neural networks. Many peptides are known to modulate the rhythmic motor patterns produced by the STG. However, in only a few cases have the mechanisms of the modulator's actions been demonstrated at the cellular level. The proposed work will investigate the biophysical mechanisms by which SDRNFLRFamide activates the pyloric and gastric rhythms in the STG and how this peptide induces some pyloric neurons to switch their activity from one rhythm to another. Following are the specific aims of this proposal. 1. Determine the specific neuronal targets of SDRNFLRFamide within the crab STG. 2. Measure the effects of SDRNFLRFamide on the ionic currents of the target neurons. 3. Mimic the effects of SDRNFLRFamide, using the dynamic clamp, to determine how the modulation of intrinsic membrane currents of the target neurons relates to the circuit effects of bath application of the peptide.